Ophthalmodynamometry (Bailliart, P., Ann.Ocul. 154: 648, 1917) was the first technique developed to determine noninvasively ophthalmic artery pressure by applying a compression on the ocular globe and by visualizing the cessation and beginning of the central retinal artery pulsations, respectively. This technique gave rise to developments of further OAP measurement procedures such as the ophthalmodynamography of Hager (Hager, Klin. Mbl. Augenheilkunde 141, 801-840, 1962) and the ocular pneumoplethysmography of Gee (Gee et al., Med. Instrum. 8, 244, 1974).
Ophthalmodynamometry gives rise to major inherent inaccuracies and technical difficulties including nontransmitted vectors of compression, movements of the globe during visualisation of the nerve head, subjectivity of the ophthalmoscopic observation of the central retinal artery pulsations and unpracticability in case of opacification of one of the refracting eye structures (Galin et al., Am. J. Ophthalmol. 67, 388, 1969).
The ophthalmodynamography of Hager, utilizing a pressure transducer in an orbital chamber, causes potential technical errors related to pressure-volume interactions with signal distortion during unvoluntary eye movements of the patients and muscle twitches and presents low correlation with systemic blood pressure (Sayegh, F., p. 163-167, in: Finke, J.(ed): Ophthalmodynamographie, Stuttgart, Schattauer Verlag, 1974).
The ocular pneumoplethysmography uses vacuum deformation of the globe by application of a vacuum of 300 to 500 mm Hg (40 to 66 KPa, resp.) upon the eye in order to rise intraocular pressure. This procedure causes subconjunctival hemorrhage and requires the instillation of local anesthetics. Furthermore, as interocular pressure cannot be directly measured, it has to be derived from calibration tables relating the applied force (negative pressure) to the value of produced intraocular pressure measured in animal experiments. This relationship is a nonlinear one and strongly dependent on the size of the eyeball that is furthermore liable to change during life time (Gee,W., Surv. Ophthalmol. 29,276, 1985). Finally, none of these methods can provide information on flow parameters.